Power recovery circuit

ABSTRACT

A power recovery circuit for use with an electron beam tube having a resonant circuit containing a capacitor in parallel with an inductive element connected to the collector of the tube. A unidirectional conducting circuit connected between the inductive element and the power supply, which supplied energy to the cathode of the tube, feeds energy back to the power supply.

United States Patent Bickert June 27, 1972 [54] POWER RECOVERY CIRCUIT [56] References Cited [72] inventor: Herbert W. Blckert, Canoga Park, Calif. UNITED STATES PATENTS [73] Assignee: The United States of America as 3,225,314 l2/l965 Rambo ..332/58 X represented by the Secretary of the Navy Primary Examiner-Benjamin A. Borchelt [22] Flled: 1965 Assistant Examiner-H. A. Birmiel [21 1 Appl No: 428,289 Attorney-G. J. Rubens and A. L. Branning ABSTRACT [52] U.S. Cl ..330/44, 330/110, 330/199 A power recovery circuit for use with an electron beam tube [51] ll.- CL i g a resonant circuit i i g a Capacitor i parallel [58] Field of Search ..3 15/239, 240, 243, 244, 254, i an inductive element connected to the collector f h tube. A unidirectional conducting circuit connected between the inductive element and the power supply, which supplied energy to the cathode of the tube, feeds energy back to the power supply.

10 Claims, 4 Drawing Figures m m- RECTIFIER 9 Le 1+ AND POWER TRANSFORMER rowan RECOVERY CIRCUIT This invention relates to a power recovery circuit for use with an electron beam tube operating at a depressed collector potential.

It has been found that the efiiciency of electron beam tubes can be increased by lowering the collector voltage below that of the electromagnetic wave interaction structure of the tube. Such collector depression has been accomplished in the past by means of power supply bias, but this method suffers from a number of disadvantages such as the requirements of a larger and more complicated power supply. In addition, this method is somewhat inefficient and results in considerable dissipation of the beam energy at the collector electrode and presents the necessity of cooling the tube if a long life expectancy is desired.

It is an object of this invention to provide improved means for operating an electron beam tube at a depressed collector potential.

It is a further object of the present invention to improve the efficiency of electron beam tubes beyond that presently available.

It is a further object of the present invention to eliminate a substantial portion of the energy dissipated at the collector electrode of an electron beam tube.

It is a further object of this invention to provide means for operating an electron beam tube with decreased power supply requirements.

The present invention accomplishes the above mentioned results by the use of improved collector circuitry comprising a resonant circuit and semiconductor diodes to feed back energy to the power supply from the collector.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the drawings in which:

FIG. 1 shows in general form the techniques of the prior art for achieving depressed collector potential operation;

FIG. 2 shows in schematic form a preferred embodiment of the present invention;

FIGS. 3 and 4 show alternative embodiments of the invention of FIG. 2.

Referring to FIG. 1, a typical scheme for depressed collector potential operation, as shown, involves circuitry comprising an electron beam tube having a cathode structure 11, a collector structure 12, and a microwave interaction structure 13. Power is supplied to the cathode structure and the microwave interaction structure by means of battery 14. Collector 12 is connected to power supply 14 by any suitable means 15. This technique, while conceptually simple, possesses a number of disadvantages among which are the need for a large power supply, and the failure to provide great efficiency of operation.

The novel power recovery circuit of FIG. 2 is to be distinguished from the depressed collector operation shown in FIG. 1 in that the latter attains a power saving by prevention of loss while the former actually provides a return of energy to the power supply. In particular, the preferred embodiment of the present invention comprises an electron beam tube 10', which may be a klystron, a traveling wave tube, or the like, and includes a cathode structure 11, a collector structure 12', and a microwave interaction structure 13, a suitable power supply 14', and power recovery circuitry 20. Power supply 14 comprises a rectifier and power transformer arrangement 16, connected to a suitable power supply filtering network 17. Power is supplied to the electron beam tube 10 by means of pulse transformer 18, the primary of which is in series with a suitable switching means such as switch tube 19, and the secondary of which is connected directly to the cathode structure 11' of the tube.

The power recovery circuit comprises a resonant LC circuit 21, including a capacitor 22 and primary 23 of transformer 27, and a suitable unidirectional conducting means 25 connected to transformer primary 23 to feedback energy to power supply filtering network 17. In addition, the power recovery circuit 20 may include a second feedback path comprising secondary 24 of transformer 27 and a second unidirectional conducting means 26 also connected to power supply filter 17. Resonant circuit 21 is tuned to the frequency of the current pulses passing through the electron beam tube, which frequency is determined by the frequency of the pulses applied to switching means 19. Resonant circuit 21 could be tuned to any harmonic of the current pulse frequency if desired, although less power will be available to be returned to the power supply at these higher frequencies.

The use of pulse transformer 18 with switching tube 19 to supply power to cathode structure 11' of the electron beam tube is not critical, for example, if a gridded traveling wave tube were employed as tube 10', the power supply and switch could be directly connected to the traveling wave tube at cathode 11.

Energy provided to network 20 may be returned to the power supply in an asynchronous and/or synchronous manner by appropriately switching on and ofi the circuit diodes 25 and 26. Asynchronous return occurs during that time interval between pulses when no current is received at the collector, and the energy stored is returned to the power supply through diode 25. Synchronous return occurs when current pulses from the collector are injected into the LC circuit and the resulting energy is returned to the power supply through diode 26. The operation of network 20 may be best thought of in terms of a sinusoidal response resulting from the application of a constant current input from collector 12' to LC circuit 21.

In order to maximize the power input, the voltage across the LC network 21 should be rectangular in shape and of highest value consistent with constant current output from collector 12'. This implies that the network 20 should provide a low resonant frequency to the collector. Accordingly, during the entire conduction period of tube 10', the collector current is fed into the low frequency circuit comprising filter capacitor 28 and winding 24 of transformer 27. This energy is passed to diode 26 so that diode 25 is not necessary unless the energy stored in the collector network at the beginning of the collector current pulse and at the end of the collector current pulse are unequal. The function of capacitor 22 is to provide with winding 23 of transformer 27 a high frequency circuit whose function is to return the collector voltage to the correct level for the next pulse. In other words, the collector voltage at the end of the collector current pulse must be approximately the complement of the voltage at the beginning of the collector current pulse, and the current in winding 23 must be different in phase. The value of capacitor 22 is chosen to conform to the pulse repetition rate, while the inductance of winding 21 is determined by the pulse duration. It is then possible to return maximum power to power supply 14' if the value of capacitor 22 exceeds that of the collector element itself and other stray capacitance. Attempts to increase the value of capacitor 22 for a given pulse length and repetition rate lead to a reduction of returnable power.

Maximum power return is achieved if the time for the voltage across capacitor 22 to reach its maximum value equals the duration of the current pulse provided to the collector. From this fact, and from a mathematical formulation of the voltage appearing across the capacitor, the values of winding 23 and capacitor 22 may be detennined. The values of capacitor 22 and winding 23 may be chosen so that power is returned either during the current pulse, or both during and after the pulse. It may be shown that a higher value for winding 23 and a lower value for the capacitor 22 is necessary if power is to be returned both asynchronously and synchronously than if power is to be returned synchronously only.

A possible difficulty exists in that the value necessary for capacitor 22 under the conditions of maximum power return may fall below the capacitance of collector element 12' and the various stray capacitances in the circuit. This, as indicated, will result in the absence of power return. However, it is possible to increase the value of capacitor 22 (and to decrease the inductance of winding 23) by having the diode 26 disconnect the low frequency circuit from the power supply during the collector period pulse at the expense of slightly decreased power return. In effect, the voltage across capacitor 22 is made to reach its maximum value at some time before the end of the current pulse. As in the case of maximum power return, the inductance of winding 23 depends on the duration of the input current pulse, however, in this case the value is affected by the time that the collector 12 is to be connected to the power supply capacitor 28. As in the case of maximum power return, the values of capacitor 22 and winding 23 may be chosen to provide either synchronous return or combined synchronous and asynchronous return of power to the power supply.

It is also possible to arrange the circuit so that collector element l2 feeds a high frequency network during the entire time of the current pulse. Possible advantages of this approach are the use of a single diode, an inductor instead of a transformer and the likelihood of less system disturbance when power is returned to the dormant power supply rather than when the power supply is itself delivering power. A possible disadvantage resides in the fact that less power is returnable by this method than by either synchronous or combined synchronous and asynchronous return. FIG. 3 shows a suitable network configuration for use with entirely asynchronous power return. It may be seen that substantial similarities exist in the circuit structure, however mathematical analysis of the currents and voltages appearing therein reveal divergence in the operation. However, as in the case of synchronous or combined synchronous and asynchronous return, a decrease in the power returned is accompanied by a corresponding increase in the value of capacitor 22' and a decrease in the inductance of winding 23'.

An alternative arrangement for entirely asynchronous operation as shown in FIG. 4 may comprise, instead of coil 23, an auto-transformer arrangement including 23" and 29. Operating characteristics of this circuit are substantially the same as that of FIG. 3 and in fact approximately the same power return is available.

In the description of all of the above networks, it has been assumed that the pulses applied to switching means 19 are of a high repetition rate, i.e., of the order I to microseconds. For long pulse length, low repetition rate operation, the circuit of FIG. 4 may be used to provide synchronous power return. Here, the transformer arrangement 23", 29 is chosen to have sufi'lcient flux linkages to support the comparatively large value of volt-seconds imposed by the long pulse length. The resulting large inductance provides a high impedance for comparatively fast tum-on of diode 25". Upon connection of the collector network to the power supply at capacitor 28", the resulting low frequency circuit including capacitor 28" maintains the turn-on voltage at almost a constant value for the duration of the current pulse. In FIG. 4, for low repetition rate, long pulse, operation capacitor 22" represents the stray capacitance associated with collector circuit 12" and no separate capacitance is necessary. Energy is transferred to power supply capacitor 28" only during the period following the turn on of diode 25". Any energy remaining in the windings of auto-transformer 23", 29, at the end of the current pulse, are dissipated by circuit damping during the comparatively long interpulse period, or else may be dissipated into a separate resistor connected to a clamping diode. It should be noted that the stray capacitor energy as well as that energy remaining in the auto-transformer during the interpulse period cannot be recovered, but this loss may be held to an acceptable level. An advantage of the operation described above, in addition to the relatively high percentage of recoverable power available, is the relative insensity to the variation in the stray capacitance represented by capacitor 22".

It should be understood, of course, that the foregoing disclosure relates only to preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for purposes of disclosure, which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. A power recovery circuit for a linearly accelerated electron beam having a cathode structure, a microwave interaction structure, and a collector structure, comprising:

a power supply connected to the cathode structure;

energy storage means connected to the collector structure;

and

means to feed back energy from the energy storage means to the power supply including unidirectional conducting means connected between said energy storage means and said power supply and poled to feed back energy from the energy storage means to the power supply.

2. The circuit of claim 1 wherein the energy storage means includes:

a resonant circuit connected between the collector structure and the feedback means.

3. The circuit of claim 2 wherein the energy storage means includes a further energy storage element coupled to the resonant circuit and to the unidirectional conducting means.

4. The circuit of claim 3 wherein the energy storage means comprises:

a transformer, the primary of which is connected to the feedback means and is also connected between the collector structure and ground, and the secondary of which is connected between the unidirectional conducting means and ground; and

a first capacitor connected across the transformer primary.

5. The circuit of claim 4 wherein the unidirectional conducting means includes a first diode connected between the transformer primary and the power supply and a second diode connected between the transformer secondary and the power supply.

6. The circuit of claim 5 wherein the power supply includes a filter capacitor connected to the first and second diodes,

the filter capacitor and the transformer forming a low frequency resonant circuit when the first diode is conducting; and

the first capacitor and the transformer primary forming a high frequency resonant circuit when the first diode is non-conducting.

7. The circuit of claim 2 wherein the resonant circuit comprises:

a first capacitor and an inductor connected in parallel between the collector structure and ground;

wherein the unidirectional conducting means comprises a diode; and

wherein the power supply includes a filter capacitor connected to the diode; and

whereby the first capacitor and the inductor provide a high frequency resonant circuit when the diode is not conductmg.

8. The circuit of claim 1 wherein the energy storage means comprises an auto-transformer structure, the primary of which is connected between the collector structure and ground;

a first capacitor connected in parallel with the auto-transfomier primary;

the secondary of the auto-transformer being connected between the ungrounded end of the auto-transformer primary and the unidirectional conducting means.

9. The circuit of claim 8 wherein the unidirectional conducting means comprises a diode connected between the auto-transformer secondary and the power supply, and wherein the power supply includes a filter capacitor connected to the diode.

10. The circuit of claim 9 wherein the first capacitor is provided by the stray capacitance of the collector structure. 

1. A power recovery circuit for a linearly accelerated electron beam having a cathode structure, a microwave interaction structure, and a collector structure, comprising: a power supply connected to the cathode structure; energy storage means connected to the collector structure; and means to feed back energy from the energy storage means to the power supply including unidirectional conducting means connected between said energy storage means and said power supply and poled to feed back energy from the energy storage means to the power supply.
 2. The circuit of claim 1 wherein the energy storage means includes: a resonant circuit connected between the collector structure and the feedback means.
 3. The circuit of claim 2 wherein the energy storage means includes a further energy storage element coupled to the resonant circuit and to the unidirectional conducting means.
 4. The circuit of claim 3 wherein the energy storage means comprises: a transformer, the primary of which is connected to the feedback means and is also connected between the collector structure and ground, and the secondary of which is connected between the unidirectional conducting means and ground; and a first capacitor connected across the transformer primary.
 5. The circuit of claim 4 wherein the unidirectional conducting means includes a first diode connected between the transformer primary and the power supply and a second diode connected between the transformer secondary and the power supply.
 6. The circuit of claim 5 wherein the power supply includes a filter capacitor connected to the first and second diodes, the filter capacitor and the transformer forming a low frequency resonant circuit when the first diode is conducting; and the first capacitor and the transformer primary forming a high frequency resonant circuit when the first diode is non-conducting.
 7. The circuit of claim 2 wherein the resonant circuit comprises: a first capacitor and an inductor connected in parallel between the collector structure and ground; wherein the unidirectional conducting means comprises a diode; and wherein the power supply includes a filter capacitor connected to the diode; and whereby the first capacitor and the inductor provide a high frEquency resonant circuit when the diode is not conducting.
 8. The circuit of claim 1 wherein the energy storage means comprises an auto-transformer structure, the primary of which is connected between the collector structure and ground; a first capacitor connected in parallel with the auto-transformer primary; the secondary of the auto-transformer being connected between the ungrounded end of the auto-transformer primary and the unidirectional conducting means.
 9. The circuit of claim 8 wherein the unidirectional conducting means comprises a diode connected between the auto-transformer secondary and the power supply, and wherein the power supply includes a filter capacitor connected to the diode.
 10. The circuit of claim 9 wherein the first capacitor is provided by the stray capacitance of the collector structure. 